Sustainable Synthesis of Silicon Precursors Coupled with Hydrogen Delivery Based on Circular Economy via Molecular Cobalt-Based Catalysts

The development of a circular economy is a key target to reduce our dependence on fossil fuels and create more sustainable processes. Concerning hydrogen as an energy vector, the use of liquid organic hydrogen carriers is a promising strategy, but most of them present limitations for hydrogen release, such as harsh reaction conditions, poor recyclability, and low-value byproducts. Herein, we present a novel sustainable methodology to produce value-added silicon precursors and concomitant hydrogen via dehydrogenative coupling by using an air- and water-stable cobalt-based catalyst synthesized from cheap and commercially available starting materials. This methodology is applied to the one-pot synthesis of a wide range of alkoxy-substituted silanes using different hydrosilanes and terminal alkenes as reactants in alcohols as green solvents under mild reaction conditions (room temperature and 0.1 mol % cobalt loading). We also demonstrate that the selectivity toward hydrosilylation/hydroalkoxysilylation can be fully controlled by varying the alcohol/water ratio. This implies the development of a circular approach for hydrosilylation/hydroalkoxysilylation reactions, which is unprecedented in this research field up to date. Kinetic and in situ spectroscopic studies (electron paramagnetic resonance, nuclear magnetic resonance, and electrospray ionization mass spectrometry), together with density functional theory simulations, further provide a detailed mechanistic picture of the dehydrogenative coupling and subsequent hydrosilylation. Finally, we illustrate the application of our catalytic system in the synthesis of an industrially relevant polymer precursor coupled with the production of green hydrogen on demand.

S4 minima (intermediates) and maxima (transition states, one imaginary frequency). Gibbs energies were computed at 298.15 K and 1 M. All frequencies below 50 cm −1 were replaced by 50 cm −1 when computing vibrational partition functions 11 with the Goodvibes script. 12 Single point calculations were performed on previous optimized geometries using the larger basis set 6-311+G(d,p) for all atoms (BS-2). 13 This freshly solution is used for the catalytic reaction, but the complex has been also isolated in order to clearly characterized the formed complex, both in solid and in solution. S5 Figure S2. Theoric ESI spectrum for the formula C17H13N3O2Co (above) and experimental ESI spectrum of isolated cat-1 which correspond with the formula C17H13N3O2Co (below).

B. General Procedure for Catalytic Hydrosilylation Reactions
0.2 mL of freshly catalyst solution (0.001 equiv.) were taken and added to a vial equipped with a stir bar, followed by olefin (0.89 mmol, 1 equiv.) and silane (0.89 mmol, 1 equiv.) resulting in formation of a dark reaction mixture. The vial was sealed with a cap and stirred at room temperature. The catalyst was removed from the reaction media by precipitating it with hexane. The solvent was evaporated and an aliquot was analyzed by 1 H NMR in CDCl3.
Attempts to purify some products, passing through a small column of silica gel, resulted in decomposition with the formation of dehydrogenated products.
The catalyst loading has been optimized. In this sense, 0.05% and 0.01% catalyst loadings have been tested. In both cases, the reaction takes place, but the reaction rate slows down. So, we have chosen 0.1% of catalyst as optimum catalyst loading.

S6
C. Substrate screening for the one-pot reaction.
The reaction was stirred for 24 hours at room temperature. 1
The reaction was stirred for 24 hours at room temperature. 1

III.
In situ, kinetic and mechanistic studies. shown in Scheme S1. It is clear that a σ-bond complex (III) can be ruled out due to the high energy as well as the decreasing Si-H stretching of -77 cm -1 . Instead, we propose a monodentate coordination of the silane to the Co via OMe (I), which presents a slight shift of +26 cm -1 . The bidentate version (II) could also be possible, but it is higher in energy.

A. Kinetic studies
Scheme S1. Computed coordination modes between silane and Co complex. S19 Figure S12. In situ Raman experiment. Cat-1 in methanol (black), Me2PhSiH (red) and the reaction mixture between cat-1 and Me2PhSiH (green).